Appended FIG. 2 is used for explaining how drive systems of a known type are constructed and operate. It is shown how the drive system comprises an electric motor 13, such as an asynchronous motor, which is connected to an electricity power supply 9 in the form of an electric power network, which typically may have a voltage of 90 VDC-400 VDC or 100 VAC-300 VAC. The system also comprises means 14 for controlling the operation of the motor by controlling relays 15 connecting the power supply 9 directly to the motor 13. It is also shown how the output shaft 16 of the motor is connected to a gear 17 connecting to a shaft 18 of a said shaft system. This drive system also comprises a mechanical brake 19 for stopping the motor at the end of a tap change operation.
This drive system has a number of shortcomings. Each new such drive system has to be custom made for the current type of tap changer, since each type of drive system is only compatible with one type of tap changer and the specific power supply voltage, which is dependent on the end customer, normally in which country the tap changer is to be used. This means that each new such drive system has a dedicated tap changer and a dedicated customer from the very beginning, which makes stocking of complete drive systems inefficient, in turn leading to long delivery times. These circumstances also force the manufacturer to keep a large amount of different components in stock for all different drive systems, which well may be a number of 20 different motors, relays, motor protectors etc. Furthermore, the mechanical brake used for stopping the movement at the end of each tap change operation requires regular service and adjustment, and it contributes to brake dust in the enclosure of the drive system, which in its turn may lead to failures in the electronic parts of the drive system.
JP 2003015747 discloses a drive system as defined in the introduction, which, however, does not address the problems mentioned above with respect to stocking of complete drive systems and keeping components for such systems in stock.